Michael and Holly share many similarities, such as their social awkwardness, sense of humour, and a history of getting ostracized by other people. Their likeness had previously made all the things that are wrong with Michael transparent to Holly, and also led to them becoming a functional couple.
When Pam set Michael up on a blind date with her landlady, it ended in a disaster. When Michael ended up dating Pam's mother, it too became a disaster. In Happy Hour, it comes off as ironic, that Pam would dare to set Michael up another time. As predicted, Michael made himself look like a fool, especially with his obnoxious clothing and behaviours.